1. Technical Field
The present disclosure relates to a motor controller, an image processing apparatus including the motor controller, and a motor control method executed by the motor controller.
2. Related Art
With image readers contained in scanners, copiers, facsimiles, and multi-function devices, and image processing apparatus, such as image forming apparatuses, accuracy in reading and forming images is ensured by accurately operating relevant movable parts.
For example, in a state in which a fixed image reader reads a document while a document feeder, such as an Auto Document Feeder (ADF), transports successive documents, a light source irradiates each transported document with light and a photoelectric conversion element such as a Charge Coupled Device (CCD) receives the light reflected from the document and photoelectrically converts the image into an electrical image signal line by line. It should be noted that the document feeder includes a driving motor and a document transport roller, and the driving motor drives the document transport roller to transport the documents at a predetermined constant speed to the image reader for reading.
In addition to the light source and the CCD, the image reader also includes a movable image reading element and a reader transport unit. When the document is placed on an exposure glass or platen, the reader transport unit, which includes a driving motor, roller, and a belt, moves the movable image reading element at a constant speed in a sub-scanning direction while the light source irradiates the document placed on the exposure glass with light and the CCD in the image reader receives the light reflected from the document to photoelectrically convert the read image into an electrical image signal line by line.
In addition, for example, in an inkjet image forming apparatus, an image is formed on a sheet of recording media by repeatedly performing an image forming process to eject ink for a predetermine number of lines and by a transport process to intermittently advance the sheet for the predetermined lines using a driving motor.
At present, direct-current (DC) motors, in particular, brushless DC motors, are widely used as the above-described driving motors.
The brushless DC motor includes a rotor having a permanent magnet but does not include a brush. Therefore, in order to detect the magnet rotor, as a position detection element, in general, a Hall IC is provided, or an inductive voltage generated in a stator coil is detected by a motor control unit and the position of the magnet rotor is estimated.
In the image processing apparatus described above, for example, in order to slacken the sheet or document, it is necessary to stop the transport of the document or sheet while the motor position is maintained as is (that is, the motor is in a position hold state). However, the driver that drives the motor based on a control signal generally deems the motor to be locked and idle when the control signal is not changed for a predetermined time period, and the driver too enters a locked state in which the driver blocks output to the brushless motor.
To solve this problem, JP-2004-324105-A discloses setting a threshold value used for determining whether the motor is a normal rotary state or the position hold state, at which point the output polarity is reversed to avoid erroneous recognition. More specifically, by setting a reversed time of an output polarity to the threshold value, it is determined that the motor is in the normal rotary state or the position hold state.
However, with this arrangement, this example cannot distinguish between the locked state determined when the control signal is not changed for a predetermined time period and the position hold state, which may erroneously recognize the hold state as the locked state. When the hold state is erroneously recognized as the locked state, the driver stops the output to the motor, such that the sheet and document cannot be hold at an intended position, and the suitable transportation cannot be performed. Therefore, it is desired to accurately distinguish between the hold state and the locked state and keep the hold state.